that should be a matter of opinion.
since really high quality heaphones use one speaker for the entire frequency response, a smaller version could be shrunken down to size.
however, the biggest problem would probably be the magnet, and more specifically the magnetic field.
when their isnt any room for the molecules/atoms to do their job at a smaller size, then the magnet needs to be redesigned.
more magnet productivity in a smaller package might come at the cost of the manufacturer having to pay more for the magnets = higher price tag for the headphones.
there doesnt have to be any comparison.. but the price tag might be all that makes the two choices different.
what is available and what is possible can sometimes be two totally different things.
i dont use in-ear headphones because they irritate my ears too much.
and if soundguruman knows the in-ear headphones aren't available on the market yet (or not available for $50 - $100) then that wouldnt really be an opinion anymore.
if they are doing lots of things with the smaller magnet, then there would be wholesale quantities for those magnets.. and that should bring the price of those magnets down.
since the bigger headphone speakers are bigger and with more room to create the design.. it isnt far-fetched to say bigger headphones are the best.
but
i wonder what those headphone magnets are doing besides being used for headphones, as there is usually some reason why the cost is cheaper.
maybe it is because they make more big-sized headphones than in-ear type.. and for that the magnets are cheaper.
i think most people find the in-ear headphones uncomfortable, bringing the bigger headphones to higher popularity.
if the in-ear headphones were made more comfortable, would the material last a long time?
would the material gather up bacteria?
would the material be washable?
this would probably add to more design, more materials, and a higher price tag for the customers.
i would love some high quality in-ear headphones sometimes.
one of those times would be laying down with my head against the pillow.
it is really hard to lay on a pillow and be comfortable with bigger headphones.
if i try and the comfort is decent, i still know that my extra weight on the headphone pad is going to flatten the pad (or cause discomfort eventually)
as the headphones also slip off the ear when tossing and turning.
in-ear headphones would take care of all of that.
there is no reason why those smaller speakers cant produce the same amount of bass similar to two 15 inch subwoofers.
decibels, or the obnoxious SPL if you dare to spend more than necessary.
they might not be the high output 15 inch speakers.. but enough is enough no?
no reason to lose your hearing sensitivity for a couple years and HOPE that it comes back.